Read on for speaker biographies and abstracts. We hope to see you on May 14th!

Quaternary Geology and Geomorphology in the Sacramento Valley, California– A Key to Assessing Levee Foundation Conditions

Janet Sowers, PhD, P.G.Fugro Consultants, Inc.
Associate Geologist

Dr. Sowers has been practicing geology and conducting research for over 30 yrs. Her technical specialties are fluvial morphology, karst processes, soil science and age dating. She holds a B.A. in Environmental Science from University of Virginia, Charlottesville, and M.A. and PhD graduate degrees in Geology from University of California, Berkeley.

Abstract – Flood protection infrastructure in California’s Sacramento Valley typically is founded on unconsolidated Late Quaternary fluvial, basin, and estuarine sediments. The stability of these sediments as foundation materials depends on characteristics such as grain size, sorting, density, permeability, bedding, and cementation, which are largely a reflection of the geologic origin and history of the sediments. This talk will discuss the development of original 1:24,000 scale mapping of Quaternary geologic units, present examples of these maps, and provide an overview of Sacramento Valley Quaternary history and geomorphology.

Ms. Wilson has been practicing consulting geology in the Bay Area for 5 years. Her technical emphasis includes geologic hazards, engineering geology and geomorphology. She holds a B.S. in Earth Sciences from the University of California Santa Cruz, and an M.S. in Geology from San Jose State University.

Abstract – The migration of water through levee foundation materials by underseepage can lead to piping and levee instability during critical high-water stages. As part of regional levee evaluation studies, a geomorphic assessment approach was developed to identify areas of potential vulnerability to underseepage along levees within the Sacramento and San Joaquin Valleys. The approach integrated existing and new Quaternary geologic mapping with soil hydrologic classes and geomorphic data to develop a criteria matrix of relative underseepage susceptibility classes (very high, high, moderate, and low). These classes were assigned to levee segments according to the criteria matrix, with late Holocene and historical channel deposits judged to have very high susceptibility, late Holocene natural levee, overbank, and crevasse splay deposits having high susceptibility, and older alluvial fan and fine-grained, basin deposits having moderate to low susceptibility. Documented past levee performance issues were also evaluated and spatially analyzed using GIS and compared to the underseepage susceptibility mapping to help calibrate the susceptibility rankings based on historical events. The GIS analysis of past performance was designed to include discrete (point) data as well as continuous (line) data. Epistemic uncertainties include the completeness and locational accuracy of the levee performance data and precision in the surficial mapping. Preliminary results suggest a strong correlation between paleochannel, historical natural levee, and peat deposits and documented levee performance issues.